Expression of a <i>Serratia marcescens</i> Chitinase Gene in <i>Sinorhizobium fredii</i> USDA191 and <i>Sinorhizobium meliloti</i> RCR2011 Impedes Soybean and Alfalfa Nodulation

Abstract

A gene encoding chitinase from Serratia marcescens BJL200 was cloned into a broad-host-range vector (pRK415) and mobilized into Sinorhizobium fredii USDA191. Chitinolytic activity was detected in S. fredii USDA191 transconjugants that carried the S. marcescens chiB gene. Chitinase-producing S. fredii USDA191 formed nodules on soybean cultivar McCall. However, there was a delay in nodule formation and a marked decrease in the total number of nodules formed by the chitinase-producing S. fredii in comparison with the wild-type strain. Expression of chitinase in S. meliloti RCR2011 also impeded alfalfa nodulation. Thin-layer chromatography of 14C-labeled Nod factors from chitinase-producing S. fredii USDA191 revealed hydrolysis of lipochitooligosaccharides.